Iran and Turkey are again voicing their opposition to a planned referendum on Iraqi Kurdish independence.

Both countries have sizable Kurdish populations of their own and share a concern that an independent Kurdistan could threaten their own territorial integrity.

Turkey’s deputy prime minister Bekir Bozdağ told a news conference that the vote violates Iraq’s constitution and threatens regional stability. The Turkish foreign minister has warned that independence could lead to civil war in Iraq.

Iranian Chief of Staff Major General Mohammad Baqeri met with his Turkish counterpart in Ankara to discuss the referendum and other regional issues.

The two countries have been waging war with Kurdish separatists for decades.

They have warned the Iraqi Kurdish leadership that following through on the referendum would have serious consequences.

The US has also asked Iraq’s Kurds to postpone the vote, saying it distracts from the ongoing fight against the Islamic State. Kurdish authorities in Erbil say the referendum will go ahead on September 25.